For example, as a radius end mill used for cutting work materials, such as a die, a radius end mill of the following structure and a cutting insert to be detachably attached to such a radius end mill of an indexable type are disclosed in Patent Document 1. This radius end mill has a tool body, and an outer periphery of a tip portion of this tool body is formed with a chip discharge flute which is spirally twisted. A planar main gash face where the angle of inclination with respect to an axis of the tool body is smaller than the helix angle of the chip discharge flute is formed on the inner peripheral side of a tip portion of the wall face of this chip discharge flute which faces the rotational direction of the tool body. An end cutting edge is formed at the tip of this main gash face, and a planar auxiliary gash face where the angle of inclination with respect to the axis is made greater than that of the main gash face and made smaller than the helix angle is formed on the outer peripheral side of the main gash face so as to be lower with respect to the main gash face via a stepped portion which extends substantially perpendicularly to the end cutting edge. A corner cutting edge which has a substantially convex circular-arc shape from the tip of this auxiliary gash face to the outer periphery thereof is connected to the outer peripheral side of the end cutting edge. An outer peripheral cutting edge is formed at a side ridge portion on the outer peripheral side of the wall face of the chip discharge flute so as to be connected to a rear end of the corner cutting edge.
In such a radius end mill, the cutting edge strength which is enough to resist cutting load can be secured by increasing the wedge angle, high sharpness can be given to the corner cutting edge, cutting resistance can be reduced. In addition, chip processability can be improved even if chips tend to get long when chips flow out, by crashing chips generated in the portion of the corner cutting edge, particularly from a protruding end of a corner portion to the outer peripheral cutting edge thereof, into the stepped portion between the auxiliary gash face and the main gash face.
[Patent Document 1] PCT International Publication No. WO 2004/058438